This invention relates generally to forming elements from aluminum alloys and more particularly to cold working nonheat-treatable aluminum alloys.
Aluminum alloys may be classified in two groups, namely nonheat-treatable and heat-treatable alloys. Nonheat-treatable alloys are hardened by a combination of alloying and strain hardening. Heat-treatable alloys are strengthened by a combination of alloying and heat treating. The strength of the nonheat-treatable materials is produced by the specific working. As the material is worked it hardens and has reduced ductility. In the heat-treatable materials, the material is worked with no or minimal increase in strength until a final heat treating process known as aging. The final product is taken to temperature for an extended period of time and then quenched. Since the heat-treatable materials remain more ductile they are generally used for products which require substantial amounts of deformation during forming. This allows the material to be worked through successive operations without intermediate thermal processing. The final physical properties are achieved through heat treatment. Thus, they are not considered applicable to the process used to form structural elements and obtain the physical strength without a heat treatment.
With the increased cost of fuel, there is a great interest in the auto industry to reduce the weight of different vehicles. Designers have been turning to the expensive, but light-weight, high strength aluminum materials to duplicate structural elements of an automobile. Heretofore, the only method of forming these structural elements was by machining casting or hot forging versus cold forming. The cold forming industry has a substantial amount of technology relative to steel but not to aluminum. The first attempt of industry to produce structural elements for use in automobiles was directed to heat-treatable alloys. Because of their strength, formability and resistance to corrosion, heat-treatable aluminum alloys were initially investigated. The lower heat tempered alloys did not have sufficient column strength to be upset and formed into the required elements and the higher tempered alloys were not ductile enough to be cold worked including upsetting followed by other subsequent cold working processes. Also to achieve the desired strength of the end-product, the total element had to be heat-treated which required excessive energy and time.
Thus there exists a need for a selection of an appropriate aluminum alloy and a process for cold working such alloy to produce an aluminum element capable of withstanding the loads for use as structural elements in automobiles.